Production of benzoic acid



Jan. 22, 1935. M. SCHARFF El AL PRODUCTION OF BENZOIC ACID Filed Aug. 14, 1929 5 Sheets-Sheet 2 5 Max chagrfode Jbhonnes AdoH Johannstin ReLchnr t INVENTORS ATTORNEY M. SCHARFF ET AL 1,988,876

PRODUCTION OF BENZOIC ACID Filed Aug. 14, 1929 Y 5 Sheets-Sheet 4 rod&

Jan. 22, 1935.

Max sohor Johannes Adolf J ol'lgnnsin Josef ReLchclr INVENTORS ATTORNEYS Jan. 22, 1935. M. SCHARFF'ET AL PRODUCTION OF BENZ-01C ACID Filed Aug. 14, 1929 5 Sheets-Sheet 5 INvENTozs Mar Scharfi Johannes Erode gdolfJohannsen osef Emcharf Patented Jan. 22, 1935 r 1 v UNITED STATES PATENT OFFICE PRODUCTION OF BENZOIC ACID 7 Max Scharfl and Johannes Brode, Ludwigshafenon-the-Rhine, Adolf Johannsen, Mannheim, and Josef Reichart, Ludwigshafen-on-the- Rhine, Germany, assig'nors to I. G. Farbenindustrie Aktiengesellschaft, Frankfort-on-the- Main, Germany, a corporation of Germany.

Application August n, 1929, Serial Ndssasss Claims. (01. 260-108) The present invention relates to the conversion ling the temperature during the decarboxylation of naphthalene into phthalic anhydride by cata need not be provided, but the gases can be lytic oxidation and also to the conversion into brought to reaction in a simple vessel filled with benzoic acid of the phthalic anhydride thus obthe catalyst, for example in'an apparatus some- 5 tained without an intermediary separation. More what similar in appearance to a shaft furnace. 5

particularly the invention relates to apparatus The conversion of the phthalic anhydride into for purifying the phthalic anhydride, thus renbenzoic acid is, however, attended with the difdering it possible to separate it in a pure state, ficulty that the catalysts are very liable to poisonwhich apparatus may also be used for the treating by sulphuric acid vapours which are formed 10 ment of the phthalic anhydride vapours with a in'the oxidation by the combustion of organic im- 10 catalyst splitting off carbon dioxide, whereby the purities containing sulphur which are present in phthalic anhydride is converted into benzoic commercial napthalene. As has been pointed out acid. Catalysts suitable for this conversion into in the said application Ser. No. 271,972, this benzoic acid are described and claimed in the poisoning action of the gases is counteracted by application for patent by Johannes Brode first contacting the gases with a catalyst which 15 and Adolf Johannsen, Ser. No. 149,520, filed has already been poisoned to some extent by sul- November 19, 1926, now Patent No. 1,955,050 of phuric acid, but which is still capable of taking April 17, 1934, and the application for patent up considerable amounts of sulphuric acid, and by Adolf J ohannsen, Ser. N 0. 385,966 filed August only then contacting the gases with fresh catalyst.

0 14, 1929. The process for the purification of This process is preferably carried out by conduct phthalic anhydride is generically described and ing the catalyst in a counter current to'thegases claimed in the U. S. Patent No. 1,693,915, granted either continuouslyor periodically. In the same December 4, 1928, to Johannes Brode and Adolf way highly active catalysts of high value can be Johannsen. A specific method of making benzoic protected by fi p s h ga s through acid, in which the gas mixture containing phthalmasses which have a substantially lower catalytic 25 ie anhydride is first passed over a purifying mass activity and are much cheaper and which take or over a catalyst for making benzoic acid, which up the sulphuric acid. Examples of such purifyis poisoned and thereby reduced in its activity, ing masses are, for example, pumice granules, forms the subject-matter of the application for zeolites and the like. In such processes it is adpatent by Johannes Brode and Adolf Johannsen, vantageous to pass at least the purifying masses 30 Ser. No. 271,972, filed April 21, 1928, now Patent in counter current to the gases and our invene No. 1,889,945 of December 6, 1932. A tion relates more particularly to apparatus for We shall now describe our invention by referconducting the catalyst or purifying masses in ence to the production of benzoic acid from counter current to the gases inareliable manner. phthalic anhydride. Our invention will be fully described with refer- 35 While the production of phthalic anhydride by ence to e ac mpa y diagrammatical d awthe catalytic oxdiation of naphthalene is a highly ings which show some forms of apparatus suit-. exothermic reaction, the conversion of the phthalable for carrying out our invention. In the said ic anhydride into benzoic acid proceeds with drawings Figure 1 represents a vertical section. I 40 only a slight disengagement of heat. Since the through one form of apparatus. Figure 2 repre- 4' gases leaving the oxidation catalyst are directly sents a plan view of one structural element of the subjected to the treatment with the catalyst splitapparatus shown in Figure 1 1. Figure 3 illusting off carbon dioxide, the phthalic anhydride trates a modified form of apparatus and Figure 4 is in a highly diluted state and the increase in is a cross-section on the line AA, Figure 3. Figtemperature in this diluted condition is only about ure 5 represents a vertical section through an- 45 20 0. when the reaction proceeds adiabatically. other form of apparatus suitable for carrying out The most favourable temperature for theconverthe aforesaid processes and Figure 6 relates to still sion into benzoic acid is slightly lower'than that another modification also shown in vertical 560-, required for the catalytic oxidation of naphthation, whereas Figur 7 i a p n Vi w Of the arlene and it is therefore possible to pass the gases 'a t Shown in Fi ure 6. 50 leaving the oxidation catalyst with a tempera- Referring first to the modificationshown in ture of about 400 C. over the catalyst capable Figure 1,1 is a cylindrical vessel which is filled of splitting off carbon dioxide directly or after witha catalyst 2. The catalyst is supported by slightly cooling them, which does not present a sieve-plate 3 which is shown in detail in Figany-difllculties in practice. Means for controlure '2. As will be seen from said Figure 2, the 56 said sieve-plate is provided with a number of large sector-shaped holes 4. Below the said sieveplate 3 there is rotatably arranged a similar sieveplate 5 also provided with sector-shaped holes. The said sieve-plate 5 can be rotated around the axle 6 by means of-the gear-wheels '7 and the handle 8. .WhenLthe apparatus is in use thetwo sieve-plates 3 and 5 are usually so positioned that the sector-shaped holes of the one plate do not coincide with those of the other plate, that is the two plates form a substantially continuous sieve supporting the catalyst. The gasesare admitted by a tube 9 and pass from the chamber 10 through the said sieves and throughthe catalyst; They are withdrawn from the upper part of the vessel 1 by a tube 11. When the catalystis to be removed from above the sieves, the lower sieve 5 is turned so that the sector-shaped holes in the.

one of the plates coincide with those in the other and the catalyst particles fall down into the chamber 10 vwherethey collect and from which they. can be, withdrawn, by means of the sluice 12. Fresh catalyst is supplied intofthe. reaction vessel by meansof a. hopper 13 and a sluice 14. In order to impart the layer of catalyst a uniform level within'the vesselll a steel-brush 15 is arranged therein which can be rotated. around the axle 16. Preferably the sluice 14'is provided with an electric heating device'which is not not shown in the drawings and by which the fresh catalyst is heated sofar, as to avoid condensation of phthalicanhydrideor benzoic acid on its surface. It will be seen that in the said construction the used catalyst, which is poisoned to some extent by sulphuric acid vapours, is always maintained in 3 the lower portion offthe vessel 1 and is brought intocontact with the gases first. Only the purified gases come into contact with the fresh catalyst present in the upper part of the vessel 1. The saidvessel'l is surrounded by a chamber 17 which serves forflheating the .vessel and catalyst when putting .the apparatus into operation. A heating medium, for example .hot combustion gases or heated aircan beadmitted into said chamber 17 by means of the tube 18 and withdrawn therefrom by the tube 20. The said chamber 17 is provided with a spiral-shaped partition 21, whereby theheating gas'is compelled to travel a screwshaped .path.

' It will be understood without further explanation that the apparatusdescribed may be modif ed in a great variety of ways without departing from the scope of our invention. For examplathe sieve-plates 3. and 5 may be provided with open ings of another shape than that of a sector, for example, they may have a circular or elliptical shape. Further the lower plate 5 need not be rotated, but the large holes in the two sieve-plates may also be brought to coincide by moving the plate 5 in a linear direction.

Sieve-plate systems constructed similar to a Venetian blind may also be used.'

Referring to Figures 3 and 4, Figure 3 illustrates a vertical section through the lowerpartof an apparatus which in its upper part is simiarm that describedin Figure 1. Corresponding parts of the apparatus shownin Figures 1 and 3 are indicated by the same reference numbers In the device shown in Figure 3 the reaction gases are admitted by the tube 9 and are divided throughout the catalyst by means of the annular chamber 22 which is free from catalyst and from which they are admitted to below a number of A shaped metal plates 23 whichservefor dividingfthem throughout the catalyst. The spent .to the downwardly directed flow of catalyst in the center of the vessel.

Referring now to the modification illustrated ,in:Figure'5, this apparatus allows of employing two different catalysts, or of one catalyst and a purifying mass, the gases being passed first through the purifying mass and then through the catalyst. The saidapparatus consists of two vertically arranged shafts 25 and 26 which may be,

.for example, of rectangular or square crosssection. Each of the said chambers is provided with sluices 27 and 28 at the upper ends and 29 and 30,,at the lower ends, which serve for-supplying the fresh catalyst or purifying mass and for withdrawing the spent masses while theapparatusis in operation. On both sides of thesaid chambersand also between them there-are arranged narrow chambers 31, 32, 33, 34 and which are connected with theshaft by the sieveplates 36, 3'7, 38, 39,.40, 41, 42, and'43. The gases to be treated are admitted into the chamber 31 by means of the tube 44 and pass through the sieve-plate 36 into the chamber 25. They pass therethrough in horizontal direction and then by the sieve-plate 3'7 into the chamber 32. From this chamber they pass through the sieve-plate 3 8 and again in the horizontal direction through themass or catalyst intheichamber 25 and leave the chamber by way --of the sieve plate 39 and the chamber 33. They next enter the chamber 26 by wayof the sieve-plate 40, pass throughthe mass in said chamber again in the horizontal direction, nextenterthe chamber 34 by way of the sieve-plate 41 andathen pass through the sieve-plate 42 again into the mass contained in the chamber 26 in the horizontal direction and are withdrawn by way of the sieve-plate 43, the chamber 35 and the tube 45. The horizontal distance between each pairof sieve-plates 36 and 37, 38 and 39, .40 and 41, 42 and 43, respectively, is smaller than thevertical distance between each two sieve-plates 36-and 39, 3'7 and 38, 40 and 43., 41- and 42, respectively, and therefore the gases pass mainly in the horizontal direction through the catalyst or purifying mass, since this direction offers the lowest resistance to the gases. Means may also be provided for passing the gas leaving the chamber 36 first through'an annular chamber 46 surroundingthe upper parts of the chambers 25 and'26, whereby the fresh catalyst or purifying mass is preheated. In the lower part of the chambers 25 and 26, there are provided resistance devices 47 and 48 which prevent the catalystn or. purifying mass from falling more rapidly in the center of each chamber than ,at the outside thereof. When the apparatus is put into operation, it may be heated by passing through hot air, or any suitable heating devices may be provided in the chambers 32 and 34.

Referring now-to the modification shown in Figures 6- and 7, the essence thereof is the arrangement of three vertical chambers 49, 50 and 51 filled with the catalyst of which two chambers are inoperation at a time while the third one is disconnected and supplied with fresh catalyst. Assuming for the sake of explanation that the chambers 49 and 50 arein operation, the flow of the gases is indicated by means of the arrows and will require no further explanation. As soon as it is noted from the composition of the gases leaving the plant that the catalyst becomes somewhat poisoned and is therefore reduced in its efllciency, the chamber 49 is shut off and the gases are passed first through the chamber 50 and then through the chamber 51 which is provided with fresh catalyst. The flow of the gases which is now established is indicated by the arrows in dotted lines. When the catalyst in the tower 50 has now become exhausted, the path of the gases is again rearranged in that the gases are now passed first through the chamber 51 and then through the chamber 49 which in the meantime has been filled with fresh catalyst. While in the arrangement shown in Figures 6 and 7 the catalyst chambers are provided in linear arrangement it is usually more advisable to arrange them at the corners of a triangle, since thereby the pipings connecting the chambers with each other become as short as possible so that losses of heat are avoided as far as possible. The said chambers may be heated before being put into operation in any suitable manner and the provision of means therefor will not present any difficulties. In the same way an arrangement may be made containing more than three chambers, for example four or even more chambers which are arranged according to the same principle and of which one is shut off at any time for replacing the spent portion of catalyst.

It may be noted here that all apparatus described in the foregoing are provided with a heat insulation in order to prevent losses of heat. This insulation is not shown in the drawings for the sake of greater clearness. Also the apparatus are provided with means for controlling the temperature which are also not shown in the drawings. In the same way as hereinbefore described for the production of benzoic acid, the apparatus may be used for the purification of phthalic anhydride by contact with solid masses absorbing sulphur compounds, as for example pumice stone, silica gel, zeolites, bauxite and the like. In such case the gases leaving the oxidation catalyst are cooled before entering the purification apparatus so far that no catalytic action of the purifying masses takes place. In this connection it may be pointed out that the said purifying masses possess to a small extent the property of splitting off carbon dioxide and of producing benzoic acid when used at high temperatures. Further the power of the said masses of absorbing sulphuric acid is higher at lower temperatures. However, the temperatures should not be so low that separation of the phthalic anhydride vapours contained in the gases takes place and the most suitable temperature is therefore about 200 C. By the separation of the sulphuric acid the formation of dark coloured condensation products of alpha-naphthoquinone during the separation of the phthalic bulk of the latter is separated as a pure white crystalline mass or powder of excellent purity.

What we claim is:

1. The process of producing benzoic acid which comprises passing the gas mixture, resulting from the catalytic oxidation of naphthalene to phthalic anhydride, directly over a catalyst splitting off carbon dioxide moved in counter-current to the gases.

2. The process of producing benzoic acid which comprises passing the gas mixture, resulting from the catalytic oxidation of naphthalene to phthalic anhydride, directly in an upward direction through a vessel through which a catalyst splitting olf carbon dioxide is moved in a countercurrent to the gases.

3. The process of producing benzoic acid which comprises passing the gas mixture, resulting from the catalytic oxidation of naphthalene to phthalic anhydride, directly over a mass capable of absorbing sulphuric acid vapors and not altering its shape or capable of giving rise to further conversion and contamination of the desired reaction product under the conditions of-working and then over a catalyst splitting oif carbon dioxide, both masses being moved in countercurrent to the gases.

4. The process of producing benzoic acid which.

comprises passing the gas mixture, resulting from the catalytic oxidation of naphthalene to phthalic anhydride, directly in an upward direction through a vessel through which a mass capable of absorbing sulphuric acid vapors and not altering its shape or capable of giving rise to further conversion and contamination of the desired reaction product under the conditions of working is moved in counter-current and then in an upward direction through another vessel through which a catalyst splitting off carbon dioxide is moved in counter-current to the gases. 5. The process of producing benzoic acid which comprises passing the gas mixture, resulting from the catalytic oxidation of naphthalene to phthalic anhydride, directly through a series of reaction vessels each of which is filled with a catalyst splitting off carbon dioxide, the contamination of said catalyst by sulphuric acid decreasing from the first to the last vessel in said series, until the catalyst in the first vessel is completely spent, then disconnecting said first vessel, arranging another vessel filled with fresh catalyst as the last of the series, and repeatin said steps.

MAX SCHARFF. JOHANNES BRODE. ADOLF JOI-IANNSEN. JOSEF REICHART. 

